This invention relates generally to the projection of film transparencies or slides, and more specifically, to automatic slide projectors having a magazine or cartridge which holds a group of slides adapted to be fed or indexed successively into a projection position.
It is widely recognized that the 35 mm slide medium has been a workhorse of the communications industry for more than forty years. This medium yields a projected screen image that is brighter, sharper, and provides greater color fidelity than any comparable medium. Moreover, slide shows are typically easier and faster to produce than motion film or video tape. An additional feature of the 35 mm slide medium is that its cost is relatively nominal when compared to the cost of video or motion picture film.
Over the last few decades, the primary instrument used to deliver the 35 mm slide image to the screen has been a carousel-type projector having a plurality of slides supported in a generally ring-shaped slide tray. Notwithstanding the wide acceptance and utilization of carousel-type projectors, there are several limitations and severe drawbacks to the use of such projectors. Indeed, the limits of the 35 mm slide medium have previously been the limits of the carousel-type projector.
More particularly, carousel-type projectors are generally very noisy due to the cumulative effect of loose slides rattling in the tray, the sounds of their electric drive motors and cooling fans, and the distinctive clatter resulting from the several mechanical arms and levers of a slide transport mechanism which inserts and retracts slides from the ring-shaped tray with respect to an underlying viewing port or gate. Bent slides generally cannot be handled by this slide transport mechanism resulting in an irritating and all-too-frequent jamming of the projector. Additionally, and possibly most importantly, the slide transport mechanism of carousel-type projectors is cumbersome and slow with a typical maximum viewing rate of about one slide per second being far too slow for the creation of highly desirable animation and/or dissolving effects. Moreover, the requirement that the slides be removed from the tray for viewing and then reinserted into the tray results in an approximately one-half second screen blackout between successive slides which is disruptive and distracting to a viewer.
In an effort to overcome some of the abovementioned problems and disadvantages of carousel-type slide projectors, many different items of auxiliary projector equipment have been developed for use with carousel-type projectors. For example there are a large number of programmers, coders, decoders, tone generators and special audio playback devices available on the market to provide synchronization of pictures and sound. Additionally, carousel-type projectors have been incorporated into multiple projection devices designed to reduce screen blackout time and to increase the maximum slide viewing rate. However, disadvantages associated with such accessories primarily include the necessity of additional capital outlays to build an acceptable system and the loss of system portability and operational simplicity following the addition of the extra equipment. Moreover, in available multiple projection devices, the images have been projected through different lenses onto a screen from different angular positions which can result in distracting visual effects and which further complicates image focusing and sizing expecially when zoom lenses are used.
Several alternative projectors have been devised which attempt to overcome the many drawbacks of the carousel-type projector. One such alternative projector is disclosed in U.S. Pat. No. 3,170,369, entitled "SLIDE PROJECTOR," issued Feb. 23, 1965. This projector utilizes a slide holder comprising a boxlike magazine having two parallel shafts therein supporting an endless flexible belt with a series of outer spring clips to receive and grip the edges of the slides to be projected. The magazine is designed to be fitted into a recess in the top of the projector so that the slides move through a substantially vertical pathway. The slide carrying magazine is also positioned relative to the optical system of the projector and coupled to its drive mechanism as an incident to insertion. To change from one group of slides to another, one magazine is removed and another is fitted into the projector in its place.
In another, more recently developed alternative projector design, the two shafts are permanently mounted in a projector in upright parallel relation to receive an unsupported floppy flexible endless belt which carries slide holding spring clips and is installed by reception through an access opening in the top of the projector. This projector design is disclosed in U.S. Pat. No. 3,799,665, entitled "SLIDE PROJECTOR WITH NON-SLIPPING ENDLESS SLIDE HOLDER," issued Mar. 26, 1974. In this projector, one of the shafts is driven step by step to feed succesive slides supported by the endless belt to a viewing gate for projection onto a screen.
The advantages realized by the utilization of endless flexible belts in connection with slide projectors include, among others, compact slide storage, smooth and rapid slide movement to a projector viewing gate, and generally jam-free operation by permitting slide viewing without requiring slide removal from the endless belt. Despite these advantages over the carousel-type projectors, previous endless belt projecting systems have had their own drawbacks and limitations. For example, satisfactory flexible, slide holding, endless belts have been difficult to manufacture at a reasonable cost. Additionally, prior cartridges and magazines for such belts have included numerous assembly parts and have been constructed in a manner denying the operator access to the slide while it is being viewed at the viewing gate. Such denial of slide access undesirably tends to make relatively difficult the process of slide loading in a predetermined order to provide a programmed slide show.
Accordingly, there has been a need for a novel slide projector which operates smoothly, quietly, rapidly and reliably and has the capability of eliminating or substantially reducing screen blackout time without requiring the use of accessory equipment. Additionally, there exists a need for a projector which permits the operator to remove and reload slides directly at the projector viewing gate without requiring removal of the cartridge or the activation of a slide transport mechanism. Further, a slide holding cartridge of the endless belt type is needed which is constructed of a minimal number of parts and which eliminates the need for accessories to obtain satisfactory results. Finally, there exists a significant need for an easily manufactured and economical slide projector which permits the simultaneous viewing of several slides and/or advancement of slides at an extremely rapid rate to achieve animation and/or dissolving effects. The present invention fulfills these needs and provides other related advantages.